A method for simultaneous measurements of cerebral blood flow (CBF) and cerebral metabolic rate for oxygen (CMRo_2) by magnetic resonance imaging (MRI) was developed.First, CBF was measured in cats by MRI,using ^<17>O-labeled water (water-17) as a tracer. Cat brain images were obtained using a fast spin-echo sequence. Intravenous infusion of water-17 and collection of a series of arterial blood samples were simultaneously performed during the MRI scan. From changes in brain signal intensity induced by water-17 infusion, water-17 concentration of brain were calculared. Water-17 concentration in arterial blood was measured directly by ^<17>O NMR spectroscopy. From these data, CBF was successfully determined using an in vivo autoradiographic strategy.Next, CBF and CMRo_2 were measured simultaneously in cats by MRI,using ^<17>O-labeled oxygen gas (oxygen-17 gas) as a tracer. Cat brain images were obtained using a fast spin-echo sequence. During inhalation of oxygen-17 gas, a series of MRI scans and arterial blood samplings were performed. From changes in brain signal intensity induced by oxygen-17 inhalation, metabolic water-17 concentration of brain were calculated. Metabolic water-17 concentration in arterial blood was measured directly by ^<17>O NMR spectroscopy. Applying convolution integral and least square method, CBF and CMRo_2 were simultaneously calculated from these data. However, the obtained values were not sufficient as reasonable values. To resolve this problem, changes in signal intensity, induced by oxygen-17 gas inhalation, should be detected much more sensitively by MRI.